Shaft interlock

ABSTRACT

A shaft interlock system may have an a interlocking piston that translates a movable locking apparatus configured to interface with a turbine shaft having a fixed locking apparatus. The movable locking apparatus may engage and disengage the fixed locking apparatus. When the movable locking apparatus is engaged with the fixed locking apparatus, the turbine shaft is only able to turn in one direction. When the movable locking apparatus is disengaged from the fixed locking apparatus, the turbine shaft is able to turn in both directions. In this way, a turbine shaft can be prevented from reverse rotation.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of, and claims priority to, and thebenefit of U.S. Ser. No. 15/076,759 filed on Mar. 22, 2016, and entitled“SHAFT INTERLOCK” which is a continuation of, and claims priority to andthe benefit of, PCT/US2014/069072 filed on Dec. 8, 2014 and entitled“SHAFT INTERLOCK,” which claims priority from U.S. ProvisionalApplication No. 61/919,545 filed on Dec. 20, 2013 and entitled “SHAFTINTERLOCK.” All three of the aforementioned applications areincorporated herein by reference in their entirety.

FIELD

The present disclosure relates to shaft interlocks, and morespecifically, to anti-reverse shaft interlocks.

BACKGROUND

Turbine engines typically windmill when idle. Often, a turbine enginewill windmill due to wind blowing through the engine. Many times, windenters through the engine outlet, causing the engine to windmill inreverse. Many turbine engines do not have a feature to prevent thereverse wind milling of the engine or utilize a complex and/or heavysystem to accomplish this feature. Moreover, forward wind milling isoften desired, for example, to enable the engine to more readily restartin flight. Reverse wind milling is not desired, for example, to reducewear on the engine when idle. A turbine engine typically has a system tofacilitate lubrication of rotating components when idle, but often thissystem only lubricates the rotating components when the engine isforward wind milling. Thus, reverse wind milling is often not desired.

SUMMARY

A shaft interlock system is disclosed having an interlocking pistonconfigured to translate a movable locking apparatus configured tointerface with a turbine shaft having a fixed locking apparatus, a mainbody wherein the interlocking piston is at least partially disposed, anextension actuator disposed in the main body and in mechanicalcommunication with the interlocking piston capable of exerting anextending force on the interlocking piston, and a retraction actuatordisposed in the main body and in mechanical communication with theinterlocking piston capable of exerting a retracting force on theinterlocking piston. The movable locking apparatus may engage the fixedlocking apparatus to permit the fixed locking apparatus and the movablelocking apparatus to slip in the axial rotation domain in a firstdirection of rotation and preventing the fixed locking apparatus and themovable locking apparatus from slipping in the axial rotation domain ina second direction of rotation.

A method of operating a shaft interlock system is disclosed includingretracting an interlocking piston having a movable locking apparatusmechanically engaged with a fixed locking apparatus of a turbine shaftby actuating a retraction actuator wherein the retracting includesinducing pressurized oil to flow into a channel of a main body of theshaft interlock system, conducting the pressurized oil through thechannel and filling a cylinder in the main body whereby the pressurizedoil exerts a force on the interlocking piston, moving the interlockingpiston inward to the main body in response to the force, mechanicallydisengaging the movable locking apparatus from the fixed lockingapparatus of a turbine shaft, permitting the turbine shaft to rotate ineither direction in response to the mechanical disengaging, extendingthe interlocking piston wherein the extending includes causing anextension apparatus to exert a force on the interlocking piston, movingthe interlocking piston outward from the main body in response to theforce, mechanically engaging the movable locking apparatus with thefixed locking apparatus of the turbine shaft, preventing the turbineshaft from rotating in one direction in response to the mechanicallyengaging.

BRIEF DESCRIPTION OF THE DRAWINGS

The subject matter of the present disclosure is particularly pointed outand distinctly claimed in the concluding portion of the specification. Amore complete understanding of the present disclosure, however, may bestbe obtained by referring to the detailed description and claims whenconsidered in connection with the drawing figures, wherein like numeralsdenote like elements.

FIG. 1 illustrates a block diagram illustrating various functionalrelationships of a shaft interlock system according to variousembodiments;

FIG. 2 illustrates various aspects of a horizontally disposed shaftinterlock system in the unlocked configuration according to variousembodiments;

FIG. 3 illustrates various aspects of a horizontally disposed shaftinterlock system in the locked configuration according to variousembodiments; and

FIG. 4 illustrates various aspects of a horizontally disposed shaftinterlock system and various surrounding hardware in the unlockedconfiguration according to various embodiments;

FIG. 5 illustrates various aspects of a horizontally disposed shaftinterlock system and various surrounding hardware in the lockedconfiguration according to various embodiments;

FIG. 6 illustrates various aspects of a vertically disposed shaftinterlock system and various surrounding hardware in the unlockedconfiguration according to various embodiments; and

FIG. 7 illustrates various aspects of a vertically disposed shaftinterlock system having a rocker arm and various surrounding hardware inthe unlocked configuration according to various embodiments.

DETAILED DESCRIPTION

The detailed description of exemplary embodiments herein makes referenceto the accompanying drawings, which show exemplary embodiments by way ofillustration and their best mode. While these exemplary embodiments aredescribed in sufficient detail to enable those skilled in the art topractice the inventions, it should be understood that other embodimentsmay be realized and that logical, chemical and mechanical changes may bemade without departing from the spirit and scope of the disclosure.Thus, the detailed description herein is presented for purposes ofillustration only and not of limitation. For example, the steps recitedin any of the method or process descriptions may be executed in anyorder and are not necessarily limited to the order presented.

Furthermore, any reference to singular includes plural embodiments, andany reference to more than one component or step may include a singularembodiment or step. Also, any reference to attached, fixed, connected orthe like may include permanent, removable, temporary, partial, fulland/or any other possible attachment option. Additionally, any referenceto without contact (or similar phrases) may also include reduced contactor minimal contact.

As used herein, phrases such as “make contact with,” “coupled to,”“touch,” “interface with” and “engage” may be used interchangeably.

In various embodiments, a shaft interlock system comprises a turbineshaft comprising a fixed locking apparatus, an interlocking pistoncomprising a movable locking apparatus, a main body, an extensionactuator, a retraction actuator, and a mounting apparatus. For example,with reference to FIG. 1, various functional relationships of an exampleshaft interlock system 100 are illustrated. A turbine shaft 70 maycomprise a fixed locking apparatus 60. An interlocking piston 40 maycomprise a movable locking apparatus 50. Fixed locking apparatus 60 maybe adapted to interlock in mechanical communication with movable lockingapparatus 50. Main body 10 may be mounted in fixed physical positionwith respect to surrounding hardware by mounting apparatus 90. Anextension actuator 20 and a retraction actuator 30 may be disposedsubstantially within main body 10. In various embodiments, extensionactuator 20 is adapted to exert an extension force on interlockingpiston 40 whereby interlocking piston 40 may be mechanically translatedpartially out of main body 10 and toward fixed locking apparatus 60. Invarious embodiments, retraction actuator 30 may be adapted to exert aretracting force on interlocking piston 40 whereby interlocking piston40 may be mechanically translated partially in to main body 10 and awayfrom fixed locking apparatus 60. In this regard, interlocking piston 40may be articulated toward or away from main body 10 and thus, away fromor toward turbine shaft 70, respectively. Interlocking piston 40 maycomprise a movable locking apparatus 50 disposed at its end.Accordingly, movable locking apparatus 50 may be translated toward oraway from fixed locking apparatus 60 of turbine shaft 70 and may engagein mechanical communication with fixed locking apparatus 60.

Having described various functional relationships of a shaft interlocksystem, with reference to FIGS. 2-5, in accordance with variousembodiments, a shaft interlock system 200 may comprise a turbine shaft71 comprising a fixed locking apparatus 61, an interlocking piston 41comprising a movable locking apparatus 51, a main body 11, an extensionactuator 21, a retraction actuator 31, and a mounting apparatus 91.Moreover, interlocking piston 41 may further comprise a cooling wand 81.

In various embodiments, a turbine shaft may comprise a spinning shaft.In various embodiments, a turbine shaft is axially traversed by a hollowchannel through which oil is conveyed. As will be discussed furtherherein, a cooling wand 81 may extend axially into this hollow channelthrough an aperture in the turbine shaft. A turbine shaft 71 may furthercomprise a fixed locking apparatus 61. In various embodiments, fixedlocking apparatus 61 is configured to mechanically interface with amovable locking apparatus 51.

In various embodiments, fixed locking apparatus 61 may comprise acastellated ring. For example, a fixed locking apparatus 61 may comprisea series of teeth disposed circumferentially about an end of turbineshaft 71 and extending axially from the end of the turbine shaft 71 in acircular plane of the surface of the turbine shaft. In variousembodiments, the teeth may comprise quadrilateral shapes, for example,square, trapezoidal or rectangular teeth. In various embodiments, theteeth may comprise triangular shapes, for example saw tooth shapesand/or right-triangle shapes.

In various embodiments, a main body 11 of a shaft interlock system 200may be mounted to an existing structure disposed in front of (in thepositive X direction) the turbine shaft 71. For example, a main body 11may comprise a mounting apparatus 91 adapted to mechanically interfacewith an existing structure via fastener apertures 92. Main body 11 maycomprise a body having an extension actuator 21 and a retractionactuator 31 disposed therein and interfaced in mechanical communicationwith interlocking piston 41. In this regard, interlocking piston may betranslated toward and away from turbine shaft 71 so that movable lockingapparatus 51 may engage and disengage from fixed locking apparatus 61.

In various embodiments, extension actuator 21 may comprise a compressedhelical spring positioned to exert a force in the negative X axisagainst interlocking piston 41. In various embodiments, retractionactuator 31 may comprise an oil channel 32 and cylinder 33 through whichoil may enter the main body 11 and exert a hydraulic force oninterlocking piston 41. In various embodiments, this hydraulic forceovercomes the force exerted by extension actuator 21 and causes theinterlocking piston 41 to translate in the positive X axis direction,thereby disengaging movable locking apparatus 51 from fixed lockingapparatus 61. As a result, when retraction actuator 31 is deactivated,for example, when the oil supply is terminated, interlocking piston 41may translate toward turbine shaft 71 so that movable locking apparatus51 engages fixed locking apparatus 61. Interlocking piston 41 mayretract away from turbine shaft 71 so that movable locking apparatus 51disengages fixed locking apparatus 61 when retraction actuator 31 isactivated, for example, when the oil supply is active. In variousembodiments, extension actuator 21 exerts 30 to 70 lbs. (˜133 to ˜312N), for example, 50 lbs. (˜223 N) of force on interlocking piston 41. Invarious embodiments, retraction actuator 31 exerts 130 to 170 lbs. (˜578N to ˜757 N), for example, 150 lbs. (˜668 N) of force on interlockingpiston 41. However, any force may be selected wherein the force exertedby extension actuator 21 is less than the force exerted by retractionactuator 31.

In various embodiments, interlocking piston 41 comprises a shaft 42extending in the X axis direction and a pressure plate 43 disposed atthe end of the shaft within the main body 11. The pressure plate 43 maycomprise a circular plate comprising an annular portion disposed in theY-Z plane within the main body 11. Interlocking piston 41 may furthercomprise O-rings 2. O-rings 2 may seal the interface betweeninterlocking piston 41 and main body 11. Retraction actuator 31 mayexert force on the pressure plate 43 thereby translating theinterlocking piston 41 along the X axis in accordance with theprinciples discussed herein.

In various embodiments, interlocking piston 41 mechanically interfaceswith a movable locking apparatus 51. In various embodiments, movablelocking apparatus 51 is connected to interlocking piston 41 viafasteners 3. In various embodiments, fasteners 3 comprise bolts,although fasteners 3 may also comprise nuts, screws, pins, welds, or anyform of permanent or detachable bonding.

In various embodiments, interlocking piston 41 further comprises acooling wand 81 extending axially through an aperture in turbine shaft71 into a hollow channel within turbine shaft 71. Lubricating oil may beconveyed from main body 11 through cooling wand 81 and introduced intoturbine shaft 71. In various embodiments, turbine shaft 71 conveys thislubricating oil to other components via a hollow channel within theturbine shaft 71. Lubricating oil introduced via cooling wand 81 maycool various components of the shaft interlock system.

In various embodiments, movable locking apparatus 51 may comprise aseries of teeth disposed circumferentially about an end of interlockingpiston 41 and extending axially from the end of the interlocking piston41 in a circular plane of the surface of the fixed locking apparatus 61.In this manner, movable locking apparatus 51 may mechanically engage anddisengage from fixed locking apparatus 61. For example, in variousembodiments, movable locking apparatus 51 comprises a castellated ring.In various embodiments, the teeth may comprise triangular shapes, forexample saw tooth shapes, or right-triangle shapes. In variousembodiments, the teeth may comprise quadrilateral shapes, for example,square, trapezoidal or rectangular teeth. The teeth of movable lockingapparatus 51 may engage with fixed locking apparatus 61 in such a manneras to permit fixed locking apparatus 61 and movable locking apparatus 51to slip in the axial rotation domain, when rotated in one direction, forexample when fixed locking apparatus 61 rotates counter clockwise, andto not slip, but to interface rigidly in the axial rotation domain, whenrotated in the other direction, for example when fixed locking apparatus61 rotates clockwise. As a result, turbine shaft 71 may be permitted torotate in one direction, for example, counter clockwise, but preventedfrom rotating in the other direction, for example clockwise, whenevermovable locking apparatus 51 is mechanically interfaced with fixedlocking apparatus 61.

In various embodiments, movable locking apparatus 51 and fixed lockingapparatus 61 comprise corresponding teeth. For example, mirror imageteeth which interlock with one another. In various embodiments, however,movable locking apparatus 51 and fixed locking apparatus 61 comprisedifferent teeth, for example, fixed locking apparatus 61 may comprisetrapezoidal teeth and movable locking apparatus 51 may compriseright-triangle teeth designed to fit into the channels between thetrapezoidal teeth of fixed locking apparatus 61. Furthermore, in variousembodiments, movable locking apparatus 51 and fixed locking apparatus 61may comprise identical teeth wherein the grooves and channels correspondand interlock. Still furthermore, in various embodiments, movablelocking apparatus 51 and fixed locking apparatus 61 may comprise clutchfaces, or any other apparatus by which axial rotation force may betransmitted such that fixed locking apparatus 61 is adapted to engagewith turbine shaft 71 and prevent rotation in a first direction whileallowing rotation in a second direction (e.g., allowing clockwiserotation while preventing counter-clockwise rotation).

In various embodiments, interlocking piston 41 comprises anti-rotationtabs 47. An anti-rotation tab comprises a finger-like extensionextending from the interlocking piston into a corresponding cavity inmain body 11. As movable locking apparatus 51 mechanically engages withfixed locking apparatus 61, fixed locking apparatus 61 may conductrotational force from turbine shaft 71, into movable locking apparatus51 and movable locking apparatus 51 may conduct rotational force intointerlocking piston 41. Anti-rotation tabs 47 conduct this force frominterlocking piston 41 into main body 11 and prevent interlocking piston41 from rotating in response to the force. In various embodiments, ashaft interlock system 200 comprises two anti-rotation tabs 47, thoughshaft interlock system 200 may comprise any number of anti-rotation tabs47 sufficient to withstand a given magnitude and impulse of force. Invarious embodiments, anti-rotation tabs 47 comprise finger-likeextensions extending from the interlocking piston, but anti-rotationtabs may comprise flanges, ridges, spline grooves, or any otherapparatus configured to prevent interlocking piston 41 from rotating.

In various embodiments, a shaft interlock system 200 may have adisengaged state and an engaged state. For example, with reference toFIGS. 2 and 4, a shaft interlock system 200 is illustrated in thedisengaged state in accordance with various embodiments. Movable lockingapparatus 51 is mechanically disconnected from fixed locking apparatus61. Interlocking piston 41 resides in a fully-retracted position,wherein the interlocking piston is translated to its farthest positionin the positive X axis direction. In this state, the force exerted byretraction actuator 31 exceeds the force exerted by extension actuator21. For example, if no oil is introduced into retraction actuator 31,then no hydraulic pressure acts on interlocking piston 41 to impel it toextend. However, retraction actuator 31 may comprise a spring, thus theretraction actuator 31 may maintain a force in the positive X directionon interlocking piston 41.

Now, with reference to FIGS. 3 and 5, a shaft interlock system 200 isillustrated in the engaged state. A movable locking apparatus 51 ismechanically connected to fixed locking apparatus 61. Interlockingpiston 41 is in a fully-extended position, wherein the interlockingpiston is translated to its farthest position in the negative X axisdirection. In this state, the force exerted by retraction actuator 31 isovercome by the force exerted by extension actuator 21. For example, ifoil is introduced into retraction actuator 31 under pressure, thenhydraulic pressure acts on interlocking piston 41 to impel it toretract. Although retraction actuator 31 may comprise a spring, thusmaintaining a force in the positive X direction on interlocking piston41, as long as sufficiently pressurized oil is introduced intoretraction actuator 31, this spring force may be overcome. In variousembodiments, extension actuator 21 exerts 30 to 70 lbs. (˜133 to ˜312N), for example, 50 lbs. (˜223 N) of force on interlocking piston 41. Invarious embodiments, retraction actuator 31 exerts 130 to 170 lbs. (˜578N to ˜757 N), for example, 150 lbs. (˜668 N) of force on interlockingpiston 41. However, any force may be selected wherein the force exertedby extension actuator 21 is less than the force exerted by retractionactuator 31. In this manner, if the oil supply fails, for example, uponturbine shutdown, the interlocking piston 41 extends so that movablelocking apparatus 51 engages fixed locking apparatus 61 and rotation ofthe shaft is prevented in one direction and allowed in the otherdirection.

Now with reference to FIG. 6, a shaft interlock system 300 isillustrated according to various embodiments. In accordance with variousembodiments, a shaft interlock system 300 may comprise a turbine shaft72 comprising a fixed locking apparatus 62, an interlocking piston 45comprising a movable locking apparatus 52, a main body 12, an extensionactuator 22, and a retraction actuator 34.

In various embodiments, a turbine shaft may comprise a spinning shaft.In various embodiments, a turbine shaft 72 may further comprise a fixedlocking apparatus 62. In various embodiments, fixed locking apparatus 62is configured to mechanically interface with a movable locking apparatus52.

In various embodiments, fixed locking apparatus 62 may comprise a seriesof teeth disposed about a circumference of turbine shaft 72 andextending radially from the circumference of the turbine shaft 72. Invarious embodiments, the teeth may comprise quadrilateral shapes, forexample, square, trapezoidal or rectangular teeth. In variousembodiments, the teeth comprise triangular shapes, for example saw toothshapes and/or right-triangle shape.

In various embodiments, a main body 12 of a shaft interlock system 300may be mounted to an existing structure disposed in front of (in thepositive X direction) the turbine shaft 72. For example, a main body 12may comprise an integral mounting apparatus (90; FIG. 1) adapted tomechanically interface with an existing structure. In variousembodiments, this integral mounting apparatus comprises the integrationof main body 12 into other bulkheads, or engine features.

Main body 12 may comprise a body having an extension actuator 22 and aretraction actuator 34 disposed therein and interfaced in mechanicalcommunication with interlocking piston 45. In this regard, interlockingpiston may be translated toward and away from turbine shaft 72 so thatmovable locking apparatus 52 may engage and disengage from fixed lockingapparatus 62.

In various embodiments, extension actuator 22 may comprise a compressedhelical spring positioned to exert a force in the positive Y axisagainst interlocking piston 45. In various embodiments, retractionactuator 34 may comprise an oil channel 35 and cylinder 36 through whichoil may enter the main body 12 and exert a hydraulic force oninterlocking piston 45. In various embodiments, this hydraulic forceovercomes the force exerted by extension actuator 22 and causes theinterlocking piston 45 to translate in the positive Y axis direction,thereby disengaging movable locking apparatus 52 from fixed lockingapparatus 62. As a result, interlocking piston 45 may extend towardturbine shaft 72 so that movable locking apparatus 52 engages fixedlocking apparatus 62 when retraction actuator 34 is deactivated, forexample, when the oil supply is terminated. Interlocking piston 45 mayretract away from turbine shaft 72 so that movable locking apparatus 52disengages fixed locking apparatus 62 when retraction actuator 34 isactivated, for example, when the oil supply is active. In variousembodiments, extension actuator 22 exerts 30 to 70 lbs. (˜133 to ˜312N), for example, 50 lbs. (˜223 N) of force on interlocking piston 45. Invarious embodiments, retraction actuator 34 exerts 130 to 170 lbs. (˜578N to ˜757 N), for example, 150 lbs. (˜668 N) of force on interlockingpiston 45. However, any force may be selected wherein the force exertedby extension actuator 22 is less than the force exerted by retractionactuator 34.

In various embodiments, interlocking piston 45 comprises a cylindricalshaft 48 extending in the Y axis direction and a pressure plate 46disposed at the end of the shaft within the main body 12. The pressureplate 46 may comprise a circular plate comprising an annular portiondisposed in the X-Z plane within the main body 12. Interlocking piston45 may further comprise O-rings 2. O-rings 2 may seal the interfacebetween interlocking piston 45 and main body 12. Extension actuator 22and retraction actuator 34 may exert extending and retracting force onthe circular plate portion thereby translating the cylindrical shaftportion of interlocking piston 42 along the Y axis.

In various embodiments, interlocking piston 45 mechanically interfaceswith a movable locking apparatus 52. In various embodiments, movablelocking apparatus 52 is an integral tip of interlocking piston 45, Invarious embodiments, movable locking apparatus 52

In various embodiments, movable locking apparatus 52 may comprise anintegral tip having a chamfered circumferential edge at the end ofinterlocking piston 45 and extending radially into the plane of rotationthrough which fixed locking apparatus 62 rotates. In this manner,movable locking apparatus 52 may mechanically engage and disengage fromfixed locking apparatus 62. For example, in various embodiments, fixedlocking apparatus 62 comprises a series of ramped teeth. In variousembodiments, the teeth comprise triangular shapes, for example saw toothshapes and/or right-triangle shapes. In this manner, teeth may engagewith movable locking apparatus 52 in such a manner as to permit fixedlocking apparatus 62 and movable locking apparatus 52 to slip in theaxial rotation domain, when rotated in one direction, for example withinfixed locking apparatus 62 rotates counter clockwise, and to not slip,but to interface rigidly in the axial rotation domain, when rotated inthe other direction, for example when fixed locking apparatus 62 rotatesclockwise. As a result, turbine shaft 71 may be permitted to rotate in afirst direction, for example, counter clockwise, but prevented fromrotating in a second direction, for example clockwise, whenever movablelocking apparatus 52 is mechanically interfaced with fixed lockingapparatus 62.

In various embodiments, as movable locking apparatus 52 mechanicallyengages with fixed locking apparatus 62, fixed locking apparatus 62 mayconduct rotational force from turbine shaft 72, into movable lockingapparatus 52 and movable locking apparatus 52 may conduct rotationalforce into interlocking piston 45. Interlocking piston 45 may conductthis force from interlocking piston 45 into main body 12 and preventinterlocking piston 45 from twisting in response to the force.

In various embodiments, a shaft interlock system 300 may have adisengaged state and an engaged state. With reference to FIG. 6, a shaftinterlock system 300 is illustrated in the engaged state. A movablelocking apparatus 52 is interfaced in mechanical communication withfixed locking apparatus 62. Interlocking piston 45 is in afully-extended position, wherein the interlocking piston is translatedto its farthest position in the negative Y axis direction. In thisstate, the force exerted by retraction actuator 34 is overcome by theforce exerted by extension actuator 22. For example, no oil or oilhaving insufficient hydraulic pressure to impel interlocking piston 42to retract, is introduced into retraction actuator 34.

Moreover, the shaft interlock system 300 may enter a disengaged state.In this state, the force exerted by retraction actuator 34 overcomes theforce exerted by extension actuator 22. For example, oil havingsufficient hydraulic pressure to impel interlocking piston 42 to retractis introduced into retraction actuator 34. Extension actuator 22 maycomprise a spring, thus maintaining a force in the positive X directionon interlocking piston 45; however, as long as sufficiently pressurizedoil is introduced into retraction actuator 34, this spring force may beovercome. In various embodiments, extension actuator 22 exerts 30 to 70lbs. (˜133 to ˜312 N), for example, 50 lbs. (˜223 N) of force oninterlocking piston 45. In various embodiments, retraction actuator 34exerts 130 to 170 lbs. (˜578 N to ˜757 N), for example, 150 lbs. (˜668N) of force on interlocking piston 45. However, any force may beselected wherein the force exerted by extension actuator 22 is less thanthe force exerted by retraction actuator 34 when sufficient pressurizedoil is introduced into retraction actuator 34. In this manner, if theoil supply fails, for example, upon turbine shutdown, the interlockingpiston 45 extends so that movable locking apparatus 52 engages fixedlocking apparatus 62 and rotation of the shaft is prevented in onedirection and allowed in the other direction.

In various embodiments, main body 12 further comprises an extension stop301, though main body 12 may comprise any number of extension stops 301adapted to limit the travel of interlocking piston 45. Extension stop301 comprises a ledge disposed within the cylinder 33 of main body 12 inwhich interlocking piston 45 travels. In this manner, the maximalextension of the interlocking piston 45 may be set, and thus the maximalapproach of movable locking apparatus 52 to fixed locking apparatus 62may be established. In various embodiments, the position of extensionstop 301 is selected to prevent movable locking apparatus 52 fromextending in the negative Y direction to ride against fixed lockingapparatus 62. In this manner, movable locking apparatus 52 may onlycontact fixed locking apparatus 62 when a tooth section of fixed lockingapparatus 62 interferes with movable locking apparatus 52, for example,though rotation. In this manner, when turbine shaft 72 (and thus fixedlocking apparatus 62) is rotating in the direction that rotation isdesired to be permitted, even if interlocking piston 45 is in itsfully-extended position, interlocking piston 42 does not continuouslycontact fixed locking apparatus 62.

In various embodiments, main body 12 further comprises a retraction stop302, though main body 12 may comprise any number of retraction stops 302adapted to limit the travel of interlocking piston 45. Retraction stop302 comprises a ledge disposed within the cylinder 33 of main body 12 inwhich interlocking piston 45 travels. In this manner, the maximalretraction of the interlocking piston 45 may be set, and thus themaximal retraction of interlocking piston 45 into the main body may beestablished, in this regard, wear on the extension actuator 22 may beameliorated by limiting the force transferred to extension actuator 22when interlocking piston 45 is in the fully-retracted position.

In various embodiments, main body 12 further comprises a cap 303. Invarious embodiments, cap 303 is a removable cap enclosing the cylinder33 of main body 12 in which interlocking piston 45 resides. Cap 303 maybe removable, for example, to replace components of extension actuator22. Moreover, cap 303 may comprise a vent 304. Vent 304 may provide arelease mechanism for oil introduced into retraction actuator 34. Inthis regard, overpressure situations may be ameliorated through theventing of hydraulic pressure from retraction actuator 34.

Now with reference to FIG. 7, a shaft interlock system 400 isillustrated according to various embodiments. In accordance with variousembodiments, a shaft interlock system 400 may comprise a turbine shaft73 comprising a fixed locking apparatus 63, an interlocking piston 49comprising a rocker arm attachment aperture 716, a rocker arm 700comprising a moveable locking apparatus 720, a main body 13, a main bodyretention apparatus 710, an extension actuator 23, and a retractionactuator 37.

In various embodiments, a turbine shaft may comprise a spinning shaft.In various embodiments, a turbine shaft 73 may further comprise a fixedlocking apparatus 63. In various embodiments, fixed locking apparatus 63is configured to mechanically interface with moveable locking apparatus720.

In various embodiments, fixed locking apparatus 63 may comprise a seriesof teeth disposed about a circumference of turbine shaft 73 andextending radially from the circumference of the turbine shaft 73. Invarious embodiments, the teeth may comprise quadrilateral shapes, forexample, square, trapezoidal or rectangular teeth. In variousembodiments, the teeth comprise triangular shapes, for example saw toothshapes and/or right-triangle shape.

In various embodiments, a main body 13 of a shaft interlock system 400may be mounted to an existing structure disposed in front of (in thepositive X direction) the turbine shaft 73. For example, a main body 13may comprise an integral mounting apparatus (90; FIG. 1) adapted tomechanically interface with an existing structure. In variousembodiments, this integral mounting apparatus comprises the integrationof main body 13 into other bulkheads, or engine features.

Main body 13 may comprise a body having an extension actuator 23 and aretraction actuator 37 disposed therein and interfaced in mechanicalcommunication with interlocking piston 49. In this regard, interlockingpiston may be translated toward and away from turbine shaft 73 so thatrocker arm 700 is translated such that movable locking apparatus 720 ismay engage and disengage from fixed locking apparatus 63.

In various embodiments, extension actuator 23 may comprise a compressedhelical spring positioned to exert a force in the positive Y axisagainst interlocking piston 49. In various embodiments, retractionactuator 37 may comprise an oil channel 38 and cylinder 39 through whichoil may enter the main body 13 and exert a hydraulic force oninterlocking piston 49. In various embodiments, this hydraulic forceovercomes the force exerted by extension actuator 23 and causes theinterlocking piston 49 to translate in the positive Y axis direction,thereby disengaging movable locking apparatus 720 from fixed lockingapparatus 63. As a result, interlocking piston 49 may extend towardturbine shaft 73 so that movable locking apparatus 720 engages fixedlocking apparatus 63 when retraction actuator 37 is deactivated, forexample, when the oil supply is terminated. Interlocking piston 49 mayretract away from turbine shaft 73 so that movable locking apparatus 720disengages fixed locking apparatus 63 when retraction actuator 37 isactivated, for example, when the oil supply is active. In variousembodiments, extension actuator 23 exerts 30 to 70 lbs. (˜133 to ˜312N), for example, 50 lbs. (˜223 N) of force on interlocking piston 49. Invarious embodiments, retraction actuator 37 exerts 130 to 170 lbs. (˜578N to ˜757 N), for example, 150 lbs. (˜668 N) of force on interlockingpiston 49. However, any force may be selected wherein the force exertedby extension actuator 23 is less than the force exerted by retractionactuator 37.

In various embodiments, interlocking piston 49 comprises a cylindricalshaft 53 extending in the Y axis direction and a pressure plate 54disposed at the end of the shaft within the main body 13. The pressureplate 54 may comprise a circular plate comprising an annular portiondisposed in the X-Z plane within the main body 13. Interlocking piston49 may further comprise O-rings 4. O-rings 4 may seal the interfacebetween interlocking piston 49 and main body 13. Extension actuator 23and retraction actuator 37 may exert extending and retracting force onthe circular plate portion thereby translating the cylindrical shaftportion of interlocking piston 42 along the Y axis.

In various embodiments, interlocking piston 49 mechanically interfaceswith rocker arm 700. In accordance with various embodiments, rocker arm700 comprises an attachment pin 718 and interlocking piston 49 comprisesa rocker arm attachment aperture 716. In various embodiments, attachmentpin 718 extends through rocker arm attachment aperture 716 whereby therocker arm is retained in mechanical communication with interlockingpiston 49 yet permitted to rotate about an axis provided by pin 718 androcker arm attachment aperture 716. In various embodiments, rocker armattachment aperture 716 is an aperture larger than pin 718, for example,oval shape, or any other shape whereby pin 718 may slidably ride in theaperture so that rocker arm 700 may smoothly articulate without unduetension. For example, as discussed further herein, rocker arm 700 may beattached to main body 13 by main body retention apparatus 710 so thatrocker arm 700 rotates axially about a substantially fixed spatiallocation in the main body retention apparatus 710. In such anembodiment, attachment aperture 716 may be implemented to permit someslidable motion to enable sufficient range of articulation of rocker arm700.

In various embodiments, rocker arm 700 is connected at one end tointerlocking piston 49, for example via rocker arm attachment aperture716 and attachment pin 718. In various embodiments, attachment pin 718may comprise a pin, a clip, a detent, or any other mechanism by whichrocker arm 700 may be retained in mechanical communication withinterlocking piston 49, yet permitted to articulate to mechanicallyengage and disengage from fixed locking apparatus 63.

In various embodiments, main body 13 may comprise a main body retentionapparatus 710 so that the rocker arm 700 rotates axially about a fixedpoint in the main body retention apparatus 710. Main body retentionapparatus 710 may comprise a thickened portion 712 of main body 13wherein an aperture permits a portion rocker arm 700 to fit inmechanical communication. For example, rocker arm 700 may furthercomprise a main body retention tab 714. Main body retention tab 714 maybe a portion of rocker arm 700 having a cross section substantiallyresembling a circle. In this manner, main body retention tab 714 may bereposed within an aperture of the thickened portion 712 of main body 13.In this manner, main body retention apparatus 710 may retain the rockerarm in mechanical communication with main body 13. Furthermore, in thismanner, compression forces exerted on rocker arm 700 by fixed lockingapparatus 63 may be transmitted to main body 13. Furthermore, in variousembodiments, main body retention apparatus 710 may comprise a aperture,a pin, a clip, a detent, or any other mechanism by which rocker arm 700may be retained in mechanical communication with main body 13, yetpermitted to rotate.

In various embodiments, movable locking apparatus 720 may comprise anintegral tip having a chamfered circumferential edge at the end ofrocker arm 700 and extending into the plane of rotation through whichfixed locking apparatus 63 rotates. In this manner, movable lockingapparatus 720 may mechanically engage and disengage from fixed lockingapparatus 63. For example, in various embodiments, fixed lockingapparatus 63 comprises a series of ramped teeth. In various embodiments,the teeth comprise triangular shapes, for example saw tooth shapesand/or right-triangle shapes. In this manner, teeth may engage withmovable locking apparatus 720 in such a manner as to permit fixedlocking apparatus 63 and movable locking apparatus 720 to slip in theaxial rotation domain, when rotated in one direction, for example withinfixed locking apparatus 63 rotates counter clockwise, and to not slip,but to interface rigidly in the axial rotation domain, when rotated inthe other direction, for example when fixed locking apparatus 63 rotatesclockwise. As a result, turbine shaft 73 may be permitted to rotate in afirst direction, for example, counter clockwise, but prevented fromrotating in a second direction, for example clockwise, whenever movablelocking apparatus 720 is mechanically interfaced with fixed lockingapparatus 63.

In various embodiments, as movable locking apparatus 720 mechanicallyengages with fixed locking apparatus 63, fixed locking apparatus 63 mayconduct rotational force from turbine shaft 73, into movable lockingapparatus 720 and movable locking apparatus 720 may conduct rotationalforce into rocker arm 700. Rocker arm 700 may conduct this force intomain body 13 and away from interlocking piston 49.

In various embodiments, a shaft interlock system 400 may have adisengaged state and an engaged state. With reference to FIG. 7, a shaftinterlock system 400 is illustrated in the engaged state. A movablelocking apparatus 720 is interfaced in mechanical communication withfixed locking apparatus 63. Interlocking piston 49 is in afully-extended position, wherein the interlocking piston is translatedto its farthest position in the negative Y axis direction. In thisstate, the force exerted by retraction actuator 37 is overcome by theforce exerted by extension actuator 23. For example, no oil or oilhaving insufficient hydraulic pressure to impel interlocking piston 42to retract, is introduced into retraction actuator 37.

Moreover, the shaft interlock system 400 may enter a disengaged state.In this state, the force exerted by retraction actuator 37 overcomes theforce exerted by extension actuator 23. For example, oil havingsufficient hydraulic pressure to impel interlocking piston 42 to retractis introduced into retraction actuator 37. Extension actuator 23 maycomprise a spring, thus maintaining a force in the positive X directionon interlocking piston 49; however, as long as sufficiently pressurizedoil is introduced into retraction actuator 37, this spring force may beovercome. In various embodiments, extension actuator 23 exerts 30 to 70lbs. (˜133 to ˜312 N), for example, 50 lbs. (˜223 N) of force oninterlocking piston 49. In various embodiments, retraction actuator 37exerts 130 to 170 lbs. (˜578 N to ˜757 N), for example, 150 lbs. (˜668N) of force on interlocking piston 49. However, any force may beselected wherein the force exerted by extension actuator 23 is less thanthe force exerted by retraction actuator 37 when sufficient pressurizedoil is introduced into retraction actuator 37. In this manner, if theoil supply fails, for example, upon turbine shutdown, the interlockingpiston 49 extends so that movable locking apparatus 720 engages fixedlocking apparatus 63 and rotation of the shaft is prevented in onedirection and allowed in the other direction.

In various embodiments, main body 13 further comprises an extension stop305, though main body 13 may comprise any number of extension stops 301adapted to limit the travel of interlocking piston 49. Extension stop305 comprises a ledge disposed within the cylinder 33 of main body 13 inwhich interlocking piston 49 travels. In this manner, the maximalextension of the interlocking piston 49 may be set, and thus the maximalapproach of movable locking apparatus 720 to fixed locking apparatus 63may be established. In various embodiments, the position of extensionstop 305 is selected to prevent movable locking apparatus 720 fromextending in the negative Y direction to ride against fixed lockingapparatus 63. In this manner, movable locking apparatus 720 may onlycontact fixed locking apparatus 63 when a tooth section of fixed lockingapparatus 63 interferes with movable locking apparatus 720, for example,though rotation. In this manner, when turbine shaft 73 (and thus fixedlocking apparatus 63) is rotating in the direction that rotation isdesired to be permitted, even if interlocking piston 49 is in itsfully-extended position, rocker arm 700 does not continuously contactfixed locking apparatus 63.

In various embodiments, main body 13 further comprises a retraction stop306, though main body 13 may comprise any number of retraction stops 302adapted to limit the travel of interlocking piston 49. Retraction stop306 comprises a ledge disposed within the cylinder 33 of main body 13 inwhich interlocking piston 49 travels. In this manner, the maximalretraction of the interlocking piston 49 may be set, and thus themaximal retraction of interlocking piston 49 into the main body may beestablished. In this regard, wear on the extension actuator 23 may beameliorated by limiting the force transferred to extension actuator 23when interlocking piston 49 is in the fully-retracted position.

In various embodiments, main body 13 further comprises a cap 307. Invarious embodiments, cap 307 is a removable cap enclosing the cylinder33 of main body 13 in which interlocking piston 49 resides. Cap 307 maybe removable, for example, to replace components of extension actuator23. Moreover, cap 307 may comprise a vent 308. Vent 308 may provide arelease mechanism for oil introduced into retraction actuator 37. Inthis regard, overpressure situations may be ameliorated through theventing of hydraulic pressure from retraction actuator 37.

Now, having described various components of shaft interlock systems andwith reference to FIGS. 1-5, a shaft interlock system 200 may be usedaccording to various methods. For example, a retraction actuator 31disposed within a main body 11 of a shaft interlock system 200 mayactuate wherein oil or other fluid may be pressurized to flow throughoil channel 32 and fill a cylinder 33 in a main body 11, and aninterlocking piston 41 may be translated so that the shaft interlocksystem enters a disengaged state. The retraction actuator 31 maymaintain a force on the interlocking piston 41 greater than acorresponding force exerted by an extension actuator 21. A turbine shaft71 comprising a fixed locking apparatus 61 may rotate in at least one ofa clockwise and a counterclockwise direction. The oil or other fluid maybe depressurized and the extension actuator 21 force exerted by theretraction actuator 31 may diminish so that the retraction actuator 31exerts a force on the interlocking piston 41 greater than that exertedby the retraction actuator 31, so that the interlocking piston 41 iscaused to translate toward a turbine shaft 71 comprising a fixed lockingapparatus 61. The translating causes a movable locking apparatus 51 tomechanically interface with a fixed locking apparatus 61. The turbineshaft 71 rotates in a counter clockwise direction, or otherwise in adesired direction of rotation, and the movable locking apparatus 51 doesnot prevent the turbine shaft 71 from rotating. The turbine shaft 71rotates in a clockwise direction, or otherwise in a undesired directionof rotation and the movable locking apparatus 51 prevents the turbineshaft from rotating.

Now, having described various components of shaft interlock systems, andwith reference to FIG. 6, a shaft interlock system 300 may be usedaccording to various methods. For example, a retraction actuator 34disposed within a main body 12 of a shaft interlock system 300 mayactuate wherein oil or other fluid may be pressurized to flow through anoil channel 35 and fill a cylinder 36 in a main body 12, and aninterlocking piston 45 may be translated so that the shaft interlocksystem 300 enters a disengaged state. The retraction actuator 34 maymaintain a force on the interlocking piston 45 greater than acorresponding force exerted by an extension actuator 22. A turbine shaft72 comprising a fixed locking apparatus 62 may rotate in at least one ofa clockwise and a counterclockwise direction. The oil or other fluid maybe depressurized and the extension actuator 22 force exerted by theretraction actuator 34 may diminish so that the retraction actuator 34exerts a force on the interlocking piston 42 greater than that exertedby the retraction actuator 34, so that the interlocking piston 42 iscaused to translate toward a turbine shaft 72 comprising a fixed lockingapparatus 62. The translating causes a movable locking apparatus 52 tomechanically interface with a fixed locking apparatus 62. The turbineshaft 72 rotates in a counter clockwise direction, or otherwise in adesired direction of rotation, and the movable locking apparatus 52 doesnot prevent the turbine shaft 72 from rotating. The turbine shaft 72rotates in a clockwise direction, or otherwise in a undesired directionof rotation and the movable locking apparatus 52 prevents the turbineshaft from rotating.

Now, having described various components of shaft interlock systems, andwith reference to FIG. 7, a shaft interlock system 400 may be usedaccording to various methods. For example, a retraction actuator 37disposed within a main body 13 of a shaft interlock system 400 mayactuate wherein oil or other fluid may be pressurized to flow through anoil channel 38 and till a cylinder 39 in a main body 13, and aninterlocking piston 49 may be translated so that the shaft interlocksystem 400 enters a disengaged state. The retraction actuator 37 maymaintain a force on the interlocking piston 49 greater than acorresponding force exerted by an extension actuator 23. A turbine shaft73 comprising a fixed locking apparatus 63 may rotate in at least one ofa clockwise and a counterclockwise direction. The oil or other fluid maybe depressurized and the extension actuator 23 force exerted by theretraction actuator 37 may diminish so that the retraction actuator 37exerts a force on the interlocking piston 42 greater than that exertedby the retraction actuator 37, so that the interlocking piston 42 iscaused to translate toward a turbine shaft 73 comprising a fixed lockingapparatus 63. The translating causes a rocker arm 700 a movable lockingapparatus 720 to mechanically interface with a fixed locking apparatus63. The turbine shaft 73 rotates in a counter clockwise direction, orotherwise in a desired direction of rotation, and the movable lockingapparatus 720 does not prevent the turbine shaft 73 from rotating. Theturbine shaft 73 rotates in a clockwise direction, or otherwise in aundesired direction of rotation and the movable locking apparatus 720prevents the turbine shaft from rotating.

Now, having described various components of shaft interlock systems andmethods of using shaft interlock systems, various components of shaftinterlock systems may be manufactured from various materials. In variousembodiments, various components of shaft interlock systems (e.g., theinterlocking piston) may comprise a austenitic nickel-chromium-basedalloy such as Inconel® which is available from Special MetalsCorporation of New Hartford, N.Y., USA, or any other high-temperaturetolerant material, for example, titanium. However, in furtherembodiments, various components of shaft interlock systems may compriseother metals, such as tungsten, aluminum, steel, or alloys, though theymay further comprise numerous other materials configured to providemechanical resiliency and/or support of the system when subjected towear in an operating environment or to satisfy other desiredelectromagnetic, chemical, physical, or biological properties such asstrength, durability, ductility, heat tolerance, thermal dissipation,and footprint constraints, among others. In various embodiments, variousportions of shaft interlock systems as disclosed herein are made ofdifferent materials or combinations of materials, and/or may comprisecoatings.

Benefits, other advantages, and solutions to problems have beendescribed herein with regard to specific embodiments. Furthermore, theconnecting lines shown in the various figures contained herein areintended to represent exemplary functional relationships and/or physicalcouplings between the various elements. It should be noted that manyalternative or additional functional relationships or physicalconnections may be present in a practical system. However, the benefits,advantages, solutions to problems, and any elements that may cause anybenefit, advantage, or solution to occur or become more pronounced arenot to be construed as critical, required, or essential features orelements of the inventions. The scope of the inventions is accordinglyto be limited by nothing other than the appended claims, in whichreference to an element in the singular is not intended to mean “one andonly one” unless explicitly so stated, but rather “one or more.”Moreover, where a phrase similar to “at least one of A, B, or C” is usedin the claims, it is intended that the phrase be interpreted to meanthat A alone may be present in an embodiment, B alone may be present inan embodiment, C alone may be present in an embodiment, or that anycombination of the elements A, B and C may be present in a singleembodiment; for example, A and B, A and C, B and C, or A and B and C.

Systems, methods and apparatus are provided herein. In the detaileddescription herein, references to “one embodiment”, “an embodiment”,“various embodiments”, etc., indicate that the embodiment described mayinclude a particular feature, structure, or characteristic, but everyembodiment may not necessarily include the particular feature,structure, or characteristic. Moreover, such phrases are not necessarilyreferring to the same embodiment. Further, when a particular feature,structure, or characteristic is described in connection with anembodiment, it is submitted that it is within the knowledge of oneskilled in the art to affect such feature, structure, or characteristicin connection with other embodiments whether or not explicitlydescribed. After reading the description, it will be apparent to oneskilled in the relevant art(s) how to implement the disclosure inalternative embodiments.

Furthermore, no element, component, or method step in the presentdisclosure is intended to be dedicated to the public regardless ofwhether the element, component, or method step is explicitly recited inthe claims. No claim element herein is to be construed under theprovisions of 35 U.S.C. 112(t), unless the element is expressly recitedusing the phrase “means for.” As used herein, the terms “comprises”,“comprising”, or any other variation thereof, are intended to cover anon-exclusive inclusion, such that a process, method, article, orapparatus that comprises a list of elements does not include only thoseelements but may include other elements not expressly listed or inherentto such process, method, article, or apparatus.

What is claimed is:
 1. A shaft interlock system comprising: aninterlocking piston configured to translate a movable locking apparatuscomprising a castellated ring configured to interface with a fixedlocking apparatus of a turbine shaft, the fixed locking apparatuscomprising a series of teeth disposed circumferentially about an end ofthe turbine shaft and extending radially from a circumference of theturbine shaft; a main body wherein the interlocking piston is at leastpartially disposed; an extension actuator disposed in the main body andin mechanical communication with the interlocking piston capable ofexerting an extending force on the interlocking piston; and a retractionactuator disposed in the main body and in mechanical communication withthe interlocking piston capable of exerting a retracting force on theinterlocking piston, wherein the interlocking piston is configured toretract in response to the retraction actuator exerting the retractionforce on the interlocking piston, wherein the movable locking apparatusis configured to engage the fixed locking apparatus to permit the fixedlocking apparatus and the movable locking apparatus to slip in the axialrotation domain in a first direction of rotation and preventing thefixed locking apparatus and the movable locking apparatus from slippingin the axial rotation domain in a second direction of rotation.
 2. Theshaft interlock system of claim 1, further comprising a cooling wandextending axially into a hollow channel of the turbine shaft.
 3. Theshaft interlock system of claim 1, wherein the extension actuatorcomprises a compressed helical spring.
 4. The shaft interlock system ofclaim 1, wherein the retraction actuator comprises an oil channelconfigured to conduct into a cylinder within the main body and thereinmay exert a hydraulic force on the interlocking piston.
 5. The shaftinterlock system of claim 1, wherein the interlocking piston comprises:a shaft; and a pressure plate disposed at the end of the shaft andwithin the main body.
 6. The shaft interlock system of claim 1, whereinthe interlocking piston further comprises an anti-rotation tab.
 7. Ashaft interlock system comprising: an interlocking piston configured totranslate a movable locking apparatus configured to interface with aturbine shaft comprising a fixed locking apparatus; a main body whereinthe interlocking piston is at least partially disposed; an extensionactuator disposed in the main body and in mechanical communication withthe interlocking piston capable of exerting an extending force on theinterlocking piston; a retraction actuator disposed in the main body andin mechanical communication with the interlocking piston capable ofexerting a retracting force on the interlocking piston, wherein theinterlocking piston is configured to retract in response to theretraction actuator exerting the retraction force on the interlockingpiston, wherein the movable locking apparatus is configured to engagethe fixed locking apparatus to permit the fixed locking apparatus andthe movable locking apparatus to slip in the axial rotation domain in afirst direction of rotation and preventing the fixed locking apparatusand the movable locking apparatus from slipping in the axial rotationdomain in a second direction of rotation; and wherein the movablelocking apparatus comprises an integral tip of the interlocking pistonhaving a chamfered circumferential edge and extending radially into aplane of rotation through which the fixed locking apparatus rotates. 8.The shaft interlock system of claim 7, wherein the main body comprisesan extension stop comprising a ledge disposed within a cylinder of themain body whereby a maximal extension of the interlocking piston isestablished.
 9. The shaft interlock system of claim 7, wherein the mainbody comprises a retraction stop comprising a ledge disposed within acylinder of the main body whereby a maximal retraction of theinterlocking piston is established.
 10. The shaft interlock system ofclaim 7, wherein the interlocking piston translates a rocker arm,wherein the rocker arm comprises the movable locking apparatus.
 11. Theshaft interlock system of claim 7, wherein the interlocking pistoncomprises the movable locking apparatus.
 12. The shaft interlock systemof claim 7, wherein the interlocking piston is configured to retract todisengage from the fixed locking apparatus in response to the retractionactuator exerting the retraction force on the interlocking piston.